I would like some help and advice with regarding to wiring up my new M60STH88-3008DF Stepper Motors (http://www.axiscnc.com/pdfdocs/M60STH88-3008DF.pdf) to my PM752 Stepper Drivers (http://www.slidesandballscrews.com/pdf/manuals/PM752.pdf).

Is it best to wire the steppers in Parallel or Series mode.

My understanding is that it's best to wire the steppers in parallel mode for more speed.

And I am having problems following the stepper motor data sheet on how to wire the steppers to my drivers.

You'll notice that the similar colours go together (remember that and you don't need to look at the instructions!)...if you swap either of the phases round the motor will spin the other way, so it's not an issue.
Before you switch the power on check the motors spin freely, as if so you've probably done it right...

Robin Hewitt

11-08-2011, 02:09 PM

Presumably you decided on parallel/series when you bought the PSU? :naughty:

Question is:- Is the high speed torque increase from wiring in parallel worth the extra heat you have to dump into the surrounding metalwork?

OTOH, if your PSU has the legs, it costs you nothing to suck it and see :tup:

You'll notice that the similar colours go together (remember that and you don't need to look at the instructions!)...if you swap either of the phases round the motor will spin the other way, so it's not an issue.
Before you switch the power on check the motors spin freely, as if so you've probably done it right...

You'll notice that the similar colours go together (remember that and you don't need to look at the instructions!)

.

NOOOOOOOOOOOOOOOOOOOOOOOOOOOO ??????????????????????????????????

Blue / white and Blue is a dead short
Same for all the others.

Gary is correct, so is the mad professor.
There are 4 ways to wire in parallel, all are correct but the motors will spin different ways.

Jonathan

11-08-2011, 05:16 PM

Whoops, sorry that was stupid! Never got it wrong on mine ... not sure why I put that.

At least if someone had followed that they'd have hopefully been saved by me saying try spinning the motor by hand. Still a totally unacceptable error. :redface:

Karl

31-08-2011, 07:28 PM

Need some help please on understanding the max current for these M60STH88-3008DF stepper motors. We have a PM542 driver that allows different currents to be set. Having read various threads and reviewed the motor calcs spreadsheet I still don't understand how to get from from the motor datasheet voltage-current values to real world values. For example, with this M60... motor the data sheet values are:

Obviously V=IxR works for the figures above; but in the real world I'm using 43vDC.

So what's the max current I should be using given my 43v supply and why am I using 43v when the data sheet says 5.46v?

Thanks

Jonathan

31-08-2011, 07:38 PM

You should set the drivers to the setting closest to (but not greater than) 2.1 amps. If you had wired them in bipolar parallel (presumably you have your reasons for not doing this) then you would set the driver to 4.2A.

The reason Ohm's law does not immediately appear to apply when using 43v is the current is pulsed, not contsant. The drivers use PWM (Pulse Width Modulation) or chopping techniques to limit the current to the motor. If you did apply 43v to the motors constantly it would quickly destroy it as that is 62 times the rated power!

You are using a higher voltage since the inductance of the motor limits the rate of change of current through the motor, and increasing the voltage counters this. Using a low voltage will limit the maximum current that can get to the motor at high step rates (since there is only a finite time for the current to rise before it is cut off at the next step), thus limiting the torque.

For an ideal inductor v(t)=Ld(i)t/dt
Rearrange that for d(i)t/dt:
d(i)t/dt=v(t)/L

We want to maximise the rate of change of current, so clearly the formula above shows that increasing the voltage or decreasing the inductance achieves this. This is why you should buy motors with the lowest inductance you can find. Putting the motors in bipolar series increases the inductance, as inductors add in series ... so in parallel the value is a quarter of the series inductance. This may explain why the torque is slightly reduced at high speed with bipolar series, though I'm only guessing.

(There's a bit more to it than that in reality, but that's the general idea.)

Robin Hewitt

31-08-2011, 11:57 PM

So what's the max current I should be using given my 43v supply and why am I using 43v when the data sheet says 5.46v?

As Jonathan says, you need it to overcome the inductance of the motor windings.

Inductance tells you how unwilling a circuit is to change the flow of current. It's all about building up and collapsing magnetic fields.

You apply 43 Volts and the current in the coil changes a jolly sight faster than if you applied 5.46 Volts. This is really useful if you want to reverse the current in a stepper coil umpteen times a second.

When it switches the current off, the coil doesn't want to stop flowing current. If you don't give that current somewhere to go the volts will simply rise until a transistor blows or ithe arcs to ground. Seriously bad idea. The fix is to allow the current to flow back to the start of the coil, round and round until the coil resistance turns it in to heat. Thus the coil inductance is a double whammy, it gets you when you turn the power on and when you turn the current off.

Luckily the driver sorts it all out for you. Some are cleverer than others though. Ignore everything on the motor label except the current.

Of course what you really need is the graph which shows motor torque over a speed range for a given current and voltage. Unfortunately the sellers of stepper motors have realised that the only thing their customers seem to care about is the holding torque so that is what they sell you. Who cares if the torque nose dives at 5rpm? It's a 3Nm motor, has to be good, dunnit!

Karl

01-09-2011, 08:34 AM

Thank you folks; most useful. Now I can't immediately remember the really good reason why I chose to wire the motors as bipolar series (there was one) but there seems to be a suggestion that bipolar parallel would be better(?). So off to find and read a thread on bipolar-series v -parallel wiring. Thanks again.

Gary

01-09-2011, 09:00 AM

Going parallel means the inductance is lower, so the driver can push the current through the phase quicker and run the motor faster.
This also means you dont need as much voltage either.
If you dont need the motor to spin fast, then go series.

Karl

01-09-2011, 09:32 AM

OK, so in terms of wiring a motor bipolar-series versus -parallel, what does 'fast' mean?

So:
If the motor data sheet gives bipolar-series 2.1A and bipolar-parallel 4.2A are those currents peak or RMS?
Given above settings, should I wire the motors Bipolar-series or -parallel (and why?) to, presumably, get the maximum torque within my desired 0-500mm/min operating range?

Thanks in advance.

Robin Hewitt

01-09-2011, 10:09 AM

there seems to be a suggestion that bipolar parallel would be better(?).

If you look at the graphs, wiring in paralel doesn't actually give you a big torque speed advantage. OTOH, experience shows you will get a lot more heat that needs to go somewhere.

Consider where you will dump that extra heat.

As I understand it, any flaws in the soft iron motor lamination act as little, shorted out, single turn, transformer coils. When you switch the motor windings you generate "eddy currents" around those flaws which heat the lamination. Halving the coil inductance boosts the eddy current heating.